1. Field of the Invention
The present invention relates to a voltage transformer for transforming a DC voltage supplied from a DC power source to a desired voltage.
2. Description of the Related Art
In recent years, hybrid vehicles and electric vehicles gain much attention as “green” vehicles.
The hybrid vehicle has a DC power source, an inverter, and a motor that is driven by the inverter, as a driving power source in addition to a conventional engine. Specifically, the hybrid vehicle obtains driving power through the operation of the engine, and by rotating the motor by using the AC voltage that is obtained by converting a DC voltage supplied from the DC power source to the AC voltage via the inverter. The electric vehicle has a DC power source, an inverter, and a motor that is driven by the inverter, as a driving power source.
With regard to the hybrid vehicles and the electric vehicles, it has been studied to boost the DC voltage supplied from the DC power source by using a buck-boost converter, and supply the boosted DC voltage to an inverter for driving a motor. Japanese Patent Application Publication No. 2004-229399 (“JP 2004-229399”) discloses a voltage transformer that supplies electric power to an electric load in such a way that an overcurrent is prevented from flowing through circuit elements even when the voltage specifying value of such a buck-boost converter suddenly increases. A related art is disclosed in Japanese Patent Application Publication No. 7-264868.
However, JP 2004-229399 does not mention a situation in which the regeneration becomes excessive due to the sudden decrease in the rotation speed of driving wheels at the time of landing after a wheel hits an obstacle on a rough road and temporarily turns free, for example. In such a case, the control stability can be worsened due to the oscillation of the inverter voltage, the battery voltage and the battery current.